1. Field of the Invention
This invention relates to a motor driven camera in which the drive source is capable at least of automatically winding up film.
2. Description of the Related Art
Recently there have been proposed a variety of motor driven cameras having motorized capabilities of winding up and rewinding film and charging the shutter. Also, a windup transmission system which enables automatic loading (hereinafter abbreviated to "AL") of the film to be carried out as well by controlling the rotation of the windup motor has been proposed by the present patent applicant. That is, in U.S. Pat. No. 4,479,705, the sprocket drives the initial stage of an AL until the takeup spool snatches up the advanced tongue of film, and, after that, the driving is switched from the sprocket to the takeup spool. Compared with the other type of windup transmission system in which both sprocket and takeup spool with a friction mechanism therebetween participate always at the same time in driving the film not only from the initial to the final stage of AL but also during the subsequent recycles of winding up, the employment of such a new type, thanks to the removal of the spool friction mechanism, can decrease the kinetic energy necessary to wind up the film and increase the framing rate and the number of fed cartridges a battery. It is also possible for the aforesaid technique to produce an additional advantage that, since, after the completion of AL, the sprocket is already become free, for the driving force of the motor is not applied to the perforations of the film, there is no possibility of tearing the film when it is tensioned as the last frame of film has been exposed.
The above-described technical idea has been realized, according to the prior art, by making use of a one-way clutch arranged in a transmission path between the sprocket and the takeup spool in combination with means for increasing the peripheral speed of the takeup spool from that of the sprocket. With this structure, however, determination of whether or not the film tongue has certainly been connected to the takeup spool when an AL cannot be made with sufficient reliability if it is relied only on examining the state of rotation of the sprocket. Hence it has been required that additional means be provided for directly detecting that the film is in motion, making the structure very complicated.
To improve this point of the above-described technical idea, the present patent applicant has also put forward a new proposal in U.S. Pat. No. 4,659,201 where the detection of a successful convolution of the film tongue on the takeup spool at a time during the AL operation is accomplished by examining whether or not the sprocket, after that time, is driven to rotate. In connection with this previous application, it should be noticed that though its claims describe the different features from those of the present one, the description of its embodiments has a reference to the detection of failure of AL, and that, besides this, several other previous patent applications whose embodiments are applied to the same systems have been filed with the U.S. Patent and Trademark Office.
According to this new proposal, a first windup transmission system of large speed reduction ratio for driving both of the sprocket and the takeup spool to rotate in a winding-up direction and a second windup transmission system of small speed reduction for driving only the spool in the winding-up direction have a common electric motor as the drive source and are selectively operated with the use of a planetary clutch. In the early stages of AL, as the aforesaid motor for winding up rotates in the normal direction, a planetary gear of the planetary clutch is in drive connection with the first transmission system. At the final stage of the AL, in order to test if the AL is successful, the rotation of the windup motor is reversed to shift the planetary gear from the first to the second windup transmission system. Since the driving by this or second windup transmission system results in rotating only the spool, leaving the sprocket free, rotation of the sprocket even in this state implies that the AL is successful, for the sprocket is driven to move by the moving film.
However, because the above-described new proposal is based on the assumption that the speed of movement of the film is changeable between low and high values for the loading and windup modes, and these values are obtained by using two transmission systems, when in application to, for example, a case of necessitating only one value of the speed, the structure becomes complicated.
Meanwhile, the present applicant has already filed, another U.S. Pat. No. 4,616,913 in which a motor driven camera has its drive source made up of two electric motors operable independently of each other for winding up or rewinding the film respectively, giving advantages that a great increase in the speed of transportation of the film becomes possible and the control of power supply to the motors only needs to switch the camera between the windup and rewind modes.
Another previous invention applied to the camera having a similar transportation mechanism to that described above has been made by the present applicant in U.S. Pat. No. 4,685,789 where the rewind drive system is provided with a changeover mechanism in the planetary gearing form (planetary clutch) so that when the reversible motor rotates in one direction, the rewinding of the film is driven, and, when in the opposite direction, the planetary clutch is operated to free the supply spool from the drive connection with the motor.
The use of such a planetary gear for allowing change of the direction of rotation of the motor to bring or take the rewind drive mechanism into or out of drive connection with the motor, though being advantageous at a simplified mode selection, gives rise to a problem that, as is encountered particularly when the planetary gear is accidentally moved by a shock or the like to set the supply spool in rigid connection with the rewind motor at a time during the blank film frame advancing for AL, the film is constrained between the fixed supply spool and the takeup spool being driven by the energized windup motor. In this case, not only the A15 is hindered from reaching completion, but also the camera cannot be unloaded without damaging the film leader. Moreover, the reloading of the camera will result only in failing again.
To avoid this problem, means may be provided for preventing the aforesaid planetary gear from changing its operative position during the advancing of blank frames of film. But, this cannot be done without involving an acceptable increase in the complexity of structure and the size of the camera.
Another solution may be suggested from one of the features in the aforesaid U.S. Pat. No. 4,685,789 which, with the aim of obtaining a load to be put in the current supply checking circuit for every one shot, is that before a camera release is actuated, current is allowed to flow to the rewind motor in a direction to disengage the planetary gear.
However, for the advancing of the blank frames of film for AL after the last of all the available frames of film has been exposed and wound up, such a solution has no effect. Differing from the usual winding operation, the AL operation moves the film in vain through a far longer length of 3 or 4 frames at a time, thus unavoidably increasing the probability for the incorrect changeover of the planetary gear to arise. And, what makes the problem especially serious is that when the incorrect changeover of the planetary gear occurs in the middle of the course of advancing the blank frames of film, the film cartridge cannot be removed from the chamber quickly and easily. Also, even after it has been removed, if the rewind motor and the rewind transmission system are left in engagement, the next AL will accidentally be interrupted with the same trouble as that described above. Thus, the failure of AL may repeat itself a large number of times.